This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/JP98/05472 which has an International filing date of Dec. 4, 1998, which designated the United States of America.
1. Field of the Invention
The present invention relates to a novel aromatic sulfonium compound, a photoacid generator comprising the same, a photopolymerizable composition and a stereolithographic resin composition comprising the said photoacid generator, and a stereolithographic process.
2. Related Art
U.S. Pat. No. 4,058,401 discloses sulfonium compounds such as phenacyl dialkyl sulfonium, or triarylsulfonium hexafluoroantimonate, and U.S. Pat. No. 4,173,476 discloses 4-(phenylthio)phenyl diphenyl sulfonium compounds as cationic polymerization initiators, respectively. And, Japanese Patent Application Laid-open No.SHO 55-125104 and 55-125105 disclose a practical method to produce a sulfonium salt as a cationic polymerization initiator to use.
Further, Japanese Patent Application Laid-open No.HEI 7-61694, 7-25922 and 7-10914 disclose sulfonium salt having a diphenylsulfide structure with a carbonyl group at 4xe2x80x2-position as a cationic polymerization initiator.
Here, as for a stereolithographic process, this process is a technique, as described in Japanese Patent Application Laid-open No.SHO 60-247515, wherein a given portion of photo-curing resin placed in a vessel is exposed continuously to a beam such as argon, helium-cadmium or semiconductor laser from above to cure the exposed portion, in order to produce a desired plane of cured layer. Then the cured layer is. overlaid with another layer of the photo-curing resin, which is then photo-cured in the same manner to produce a second cured layer which continuously overlaps the first layer; and the same process is repeated to finally obtain a desired three-dimensional solid shape.
As resins previously used for the above-described stereolithographic process, mention may be made of radically polymerizing resin compositions and, for example, Japanese Patent Application Laidxe2x80x94open No.HEI 2-228312 and No.HEI 5-279436 disclose a stereolithographic resin composition composed mainly of (meth)acrylic resin. Further, Japanese Patent Application Laid-open No.HEI2-145616, with the aim of reducing deformation, discloses a stereolithographic resin which contains liquid resin and fine particles whose difference in apparent specific gravity is less than 0.2. For producing moldings at higher precision, a composition comprising an unsaturated ethylene-derivative monomer, a photo-initiator, and a potentially insoluble, potentially radioactive polarizing substance is reported in Japanese Patent Applications Laid-open No.HEI 3-15520, and a composition comprising an unsaturated ethylene-derivative monomer, a photo-initiator, and a potentially soluble radio-polarizing substance is reported in Japanese Patent Applications Laid-open No.HEI 3-41126. In addition, Japanese Patent Application Laid-open No.HEI 4-85314 discloses a resin composition comprising a silicone urethane acrylate, a compound having multifunctional ethylenic unsaturated bonds, and a polymerization initiator.
Besides the above-mentioned radically polymerizable resin composition, another stereolithographic resins are known cationically polymerizing resin composition. For example, Japanese Patent Application Laid-open No.HEI 1-213304 discloses an invention characterized by comprising a cationically polymerizing energy beam curable organic compound and a energy beam sensitive cationic polymerization initiator. Japanese Patent Application Laid-open No.HEI 2-28261 discloses a resin comprising a cationically polymerizing energy beam curable organic compound and a portion of a radically polymerizing radio-curing organic compound, which exhibits reduced shrinkage and improved resolution. Also, Japanese Patent Application Laid-open No.HEI 2-80423 discloses a resin composition comprising an epoxy resin, a vinyl ether resin, an energy beam sensitive cationic polymerization initiator, a radically curing resin, and an energy beam sensitive radical polymerization initiator. In addition, Japanese Patent Application Laid-open No.HEI 2-75618 discloses a stereolithographic resin composition characterized by comprising a cationically polymerizing energy beam curable organic compound, an energy beam sensitive cationic polymerization initiator, a radically polymerizing energy beam curable organic compound, an energy beam sensitive radical polymerization initiator, and a polyester having hydroxyl groups.
Further, Japanese Patent Application Laid-open No.HEI 9-87311, 9-278935 and 10-168107 disclose stereolithographic resins using a sulfonium salt having a diphenylsulfide structure with a benzoyl group at 4xe2x80x2-position as a photo-initiator.
However, the compound disclosed by above mentioned U.S. Pat. No. 4,058,401 can sensitize to the shortwave radiation of a mercury lamp applied usually as source of a radiation, but when the compound is used with an epoxy resin, etc., the ultraviolet ray which is necessary to activate an initiator, is intercepted owing to absorption of radiation by the resin itself and it becomes difficult to obtain a satisfactory curing performance.
In order to solve this problem, U.S. Pat. No. 4,173,476 and Japanese Patent Application Laid-open Nos. SHO 55-125104, and 55-125105 disclose the use of a sulfonium salt being able to absorb a long-wave radiation shifted, but a satisfactory curing performance is not obtained yet.
In addition, Japanese Patent Application Laid-open Nos. HEI 7-61694, 7-25922 and 7-10914 disclose sulfonium salt having a diphenylsulfide structure with a carbonyl group at 4xe2x80x2-position as a cationic photo-polymerization initiator, and the composition applied this compound is repported to show good storage stability, good compatibility with vinylether, good hardening and little smell of cured article, but the curing performance is insufficient.
Further, any of a radically polymerizing resin and a stereolithographic resin composition composed mainly of it is suffered from the hindrance to curing by oxygen, which results in low degree of cure on curing, so that it is necessary to carried out xe2x80x9cpost cure processxe2x80x9d by ray or heat, which is necessarily concerned in curing of mold. In the post cure process, however, the moldings has such a disadvantage as being apt to deform. Further, these resins show large shrinkage on curing, which makes it difficult to obtain a molding with desirable dimension.
Furthermore, cationically curable stereolithographic resins as described above in Japanese Patent Application Laid-open No.HEI 1-213304, No.HEI 2-28261 and No.HEI 2-75618, have such superior characteristic properties that the post cure process are not necessary and the deformation are little, as the curing proceeds through an active group even after the beam to be exposed are shut down, and it can also easily give shaped articles having desired sizes by virtue of small shrinkage on curing. However, these resins have such disadvantages that they have insufficient sensitivity to an energy beam to be exposed, and the cured articles show insufficient mechanical properties.
And also, in the invention disclosed by Japanese Patent Application Laid-open Nos. HEI 9-87311, 9-278935 and 10-168107mentioned above, they have insufficient sensitivity to an energy beam to be exposed.
Therefore, the object of the present invention is to provide a novel compound usefull as a suitable photo-polymerization initiator being able to give a good cured article rapidly by effective absorption of the radiation from the source of a ray, photoacid generator comprising the novel compound and photopolymerizable compositions comprising the same.
And another object of the present invention is to provide a stereolithographic resin compositions, by which the above mentioned disadvantages of the prior art can be overcome, by which the prevention of curing under oxygen do not occur and a molding with desirable dimension can be obtained easily, having sufficient sensitivity to an energy beam to be exposed and to provide a stereolithographic process using the said resin composition.
The inventors have, after thorough study, succeeded to synthesize the novel aromatic sulfonium compound of the general formula (I), and have found that the said compound has good compatibilities to various resins, and is activated by effective absorption of long-wave radiation, therefore, the photo-polymerizable composition comprising the said compound can be cured rapidly to give good cured articles, and also the photo-resist comprising the same has good sensitivity and good resolution, to finally complete the present invention.
Further, the inventors have found that, when a stereolithographic resin composition comprising an aromatic sulfonium salt compound of the following general formula (I) as an energy beam sensitive cationic polymerization initiator, with a cationically polymerizing organic substance is applied to stereolithographic process by exposing to a certain specific energy beam, this resin composition do not suffer from the hindrance to curing by oxygen, can easily give shaped articles having desired sizes by virtue of the high accuracy thereof in curing, owing to the high sensitivity thereof for radiant energy, to finally complete the present invention.
That is, the present invention is an aromatic sulfonium compound expressed by a general formula (I), 
wherein, R1 is a p-phenylene group, in which one or more hydrogen atoms are substituted by halogen or alkyl group, R2 is a hydrocarbon radical, in which oxygen or halogen may be contained, Y1 and Y2 are identical or different, respectively hydrogen, halogen or oxygen, or a hydrocarbon radical, in which oxygen or halogen may be contained, X is a group of atoms, which can form a monovalent anion.
The present invention is also a photoacid generator comprising the aforementioned aromatic sulfonium compound.
Further, the present invention is a photo-polymerizable composition comprising the aforementioned photoacid generator.
Furthermore, the present invention is a stereolithographic resin composition comprising,
(1) cationically polymerizing organic substance, and
(2) photoacid generator mentioned above as an energy beam sensitive catioenic polymerization initiator.
Still furthermore, the present invention is a stereolithographic process, wherein a given portion of the aforementioned stereolithographic resin composition is exposed to the beam in order to produce a desired thickness of cured layer, the energy of the beam with an emission wave length of 345 to 360 nm being not less than 70% based on the total energy of the beam with an emission wave length of 250 to 400 nm to cure the exposed portion thereof; then, the cured layer is overlaid with another layer of the stereolithographic resin composition, which is then cured in the same manner to produce a second cured layer which continuously overlaps the first layer, and the same process is repeated to finally obtain a three-dimensional molding.
In addition, the resin composition can contain,
(3) radically polymerizing organic substance, and
(4) energy beam sensitive radical polymerization initiator as essential components.
The stereolithographic resin composition according to the present invention can contain an organic compound containing two or more hydroxyl groups in a molecule as an optional component.